Observation of migrating superoxide species in YBa 2Cu 3( 57Co)O 7−δ

Abstract

The interaction of the migrating superoxide ion O − 2 with the central cobalt-57 atom of the four coordinate species at the chain site is probed with the help of emission Mössbauer spectroscopy. The bond formation between 57Co and O − 2 requires some thermal activation, and consequently the five-coordinate species is stable only above ∼ 350 K. The equilibrium shifts in its favor at higher temperatures, and the interconversion between the two species is completely reversible. The O − 2 ion can either attach to cobalt end-on with one of the oxygen atoms or interact equivalently with both. The amount of the five-coordinate species formed seems to be limited by the availability of O − 2. The interconversion ceases to occur after a prolonged thermal treatment of the YBa 2 Cu 3( 57 Co) O 7−δ pellet at 420°C under argon flow. All the interstitial oxygen species are presumably removed without any measurable loss of oxygen from the Cu-O chains.